He is interested in how plants resist disease, and in how resistance is overcome by pathogens. To suppress host defence, pathogens secrete effector proteins into plant cells or into their apoplastic spaces. How these effectors work, and the identity of their targets in the host, help us understand plant defence mechanisms.He work on the following problems:How do plant NB-LRR disease resistance proteins recognize pathogen effectors and then activate defence; What are the effectors of the Arabidopsis downy mildew and white rust pathogens (Hyaloperonospora arabidopsidis and Albugo sp), and how do they suppress host defences;Can we find and clone new sources of resistance to potato late blight from wild Solanum species.